In one of her most candid interviews, Fonda, 73, happily tells of taking the libido-boosting hormones and advises other women to try what is still a controversial treatment.

"Here's something I haven't said publicly yet: I discovered testosterone about three years ago, which makes a huge difference if you want to remain sexual and your libido has dropped," she says.

"Use testosterone. It comes in a gel, a pill or a patch."

But she adds: "I had to stop because it was giving me acne. It's one thing having plastic surgery, but it is quite another to have adolescence acne. That is going too far.'

The double Oscar-winning actress, who became a sex symbol through the risqué 1960s classic Barbarella, uses 50 pages of her new volume of autobiography, Prime Time, to explain how the passage of time need not dampen a couple's ardour.

The chapter is entitled 'The Changing Landscape of Sex when You're Over the Hill', and offers 'some suggested readings, videos and sex shops.'

The book does not, however, reveal her own use of libido-boosting testosterone.

The actress, currently in a relationship with the music producer Richard Perry – who is four years her junior - once put her enduring good looks down to 10 per cent plastic surgery, 30 per cent genes, 30 per cent lifestyle, and 30 per cent "good sex".

Fans of Barbarella may also find her use of sexual boosts was echoed in the 1968 sci-fi film where a scantily-clad Fonda encountered such devices as the Excessive Machine, which could drive a victim to death by pleasure.

This was five years before Woody Allen tried the Orgasmatron in his 1973 comedy Sleeper.

The love life advice is the latest in a long career of offering tips on self-improvement to her fans.

Fonda was a pioneer of exercise videos for women - although she later admitted to having cosmetic surgery to help maintain her appearance.

Her promotion of testosterone may prove controversial.

Testosterone replacement, which is usually administered to women in the form of a gel or patch, has caused a furore in the US.

Critics argue that drugs companies have profited by medicalising a problem whose real causes may lie in psychological or relationship issues.

In the UK, testosterone treatment is licensed for women who have had their ovaries removed, are already on oestrogen and have low libido.

Claudine Domoney, the chairwoman of the UK's Institute of Psychosexual Medicine, said that women produce testosterone naturally, although in much lower quantities than men, and acne and body hair growth remain rare side effects of female testosterone replacement.

She warned that the precise long-term risks are not yet fully known.

Other Hollywood stars also appear to have tried testosterone.

In June, Robbie Williams, 37, the British singer, admitted a Hollywood doctor persuaded him to try testosterone to counter lethargy.